Railway-train-control system



May 14, 1929. T. E. CLARK ET AL RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 5. 1925 14 Sheets$heet 1 2! life MM 50@ w m m T f R W5 0 Z 5 6N0 A 0 l u 0 5 Z Y 7 0O B L May 14, 1929.

T. E. CLARK ET AL RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 5. 1925 14 Sheets-Sheet 2 INVENTORS Thomas E C/ar/f James E. C/ark BY IMWLQQM ATTORNEYS Filed Deb. 5. 1925 14 Sheets-Sheet 3 ATTORNEYS May 14, 1929. T. E. CLARK ET AL RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 5, 1925 14 Sheets-Sheet 4 1 INVENTOR'S Y Y Thomas ETC/ark kTamra: .C/ark BY 2 Z ATTORNEYS May 14, 1929. T. E. CLARK ET AL RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 5. 1925 14 Sheets-$heet 5 INVENTORS- 7770mm; 5 C/a/k \BlYames E. C/ark 71%; M M. v

ATTORNEYS May 14, 1929.

T. E. CLARK ET AL 1,712,981

RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 5. 1925 14 Sheets-Sheet 6 I 5 f z 57. J a I gz fi I ATTORNEYS May 14, 1929. CLARK ET AL 1,712,981

RAILWAY TRAIN CONTROL SYSTEM Filed Dec 5. 1925 14 Sheets-Sheet INVENTORS 7 /0/1705 5. (/ar/r {Q0765 EC/ark ATTORNEYS T. E. CLARK ET AL v RAILWAY TRAIN CONTROL SYSTEM May 14, 1929.

14 Sheets-Sheet 8 Filed Dec. 5, 1925 M MU u INVENTORS f. C/fir/f- Thomas James A.

ATTORNEYS May 14, 1929.

T. E. CLARK ET AL RAILWAY TRAIN CONTROL SYSTEM 4 Sheets-Sheet 9 Filed Dec. 5. 1925 INVENTOR5 homas E.C/0rk James E. 6/ar/r BY ATTORNEYS May 14, 1929. T, E, CLARK ET AL 1,712,981

RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 1925 14 Sheets-Sheet l0 INVENTORS ATTORNEY5 May 14, 1929. CLARK ET AL 1,712,981

RAILWAY TRAIN CONTROL SYSTEM Filed Dec. 1925 I 4 Sheets-Sheet INVENTORS 772001055. C/a/A James .E, C/ar/r ATTORNEY May 14, 1929. CLARK ET AL 1,712,981

RAILWAY TRAIN CONTROL SYSTEM INVENTORS ZZM/ fl m ATTORNEYS T. E. CLARK T AL RAILWAY TRAIN CONTROL SYSTEM May 14, 1929.

Fild Dec. 5. P325 l4 Sheets-Sheet 15 /5 6 M m5 R N sf 0 w n mmm A m May 14, 1929. T. E; CLARK ET AL 1 1,712,981

' RAILWAY TRAIN CONTROL SYSTEM 14 Sheets-Sheet 1 4 Filed Dec. 5. 1925 INVENTORS 7770mm; 5. (/ark' Wes A. (/ark ATTORNEYS Patented May 14, 1929.

UNITED STATES PATENT OFFICE.

gnomes E. cLARK Aim JAMES E. own, or DETROIT, moment, AssIeNoRs 'ro oonrrnuons TRAIN conrnor. coaronnrron, or DETROIT, MICHIGAN, A CORPORA- TION OF MICHIGAN.

.RAILWAY-TRAIN-CON'IROL SYSTEM.

Application filed December 5, 19215. Serial No. 73,318.

This invention relates to train control systems and more particularly to arrangements cooperating with block signalling systems to control the movement of trains.

It has been proposed to employ low frequency inductive control arrangements in former train control systems but such systems in highly congested traflic areas, where there is the greatest need for train. control,

I to are unreliable due to the wide prevalence offoreign currents of low frequency.

lln connection. with former systems it has also been proposed to employ a receiving system on a vehicle or train including an electromagnetic device or a hot wire mechanism but these arrangements require alarger amount of current to be introduced into the track circuit from the wayside stations than is convenient under all circumstances. an in accordance with the present invention, it is proposed to incorporate a high frequency signalling arrangement in combination with a block signalling system for the control of trains. '1 Another feature of the invention resides in the use of an electron discharge device on a moving vehicle or train, to control electropneumatic brake mechanism for stopping trains under predetermined conditions.

Other features of the invention will appear from the detaileddeseription and ap pended claims.

In the drawings, Figs. 1 1 1 andv 1, when arranged from right to left in the order 3 named, diagrammatically represent a portion of a railway system divided into four block sections on certain of which sections or other signal collector to ensure application of the brakes in the event that the circuit of the loop or signal collector'is broken or otherwlse placed in an inoperative condition.

Fig. 4 is a side elevationof-a locomotive equlpped with a receiving unit for controlling the air-brake system.

Fig. 5 1s a partial front elevation ofa locomotive With certain parts broken away to indicate the location and inclination of the coils on the locomotive with respect to the energized rails of the track section.

Figs. 6 and 7 are diagrams representing the magnetic field about the track rails, as well as the loop collector coils and also the locomotive wheels and axle.

F gs. 8 and QIGDIGSBIlt an elevation and a section, respectively,of an electrical circuit controller arranged to disable the electrical train control devices when the locomotive is operating in non-signalling territory, such as at the round-house, various sections of the freight yard or other territory without control equipment.

Fig. 1 0 is a sectional view of an electro'-' pneumatic valve mounted on the locomotive and adapted to be variably operated by the I'GCGlVlllgdQVlCG to control the air brake system of the train.

Fig. 11 shows the general arrangement of the receiving device together with the electrically controlled pneumatic valve and a portion of the air system all mounted on the locomotive.

Figs. .12 and 13 are sectional diagrams in which Fig. 12 shows the air brake equipmentin normal running position and Fig. 13 shows the an brake equipment in condition to apply the brakes. Y i

Fig. 14 is a sectional view showing the air brake reduction valve.

Referring to: the drawings, 1 to 1 inelusive, the track rails 1 and 2, which are elec trio-ally bonded together, are shown divided into sections by'insulatingjoints3. Adjacent each junction of two sections, there is provided a wayside station such as A, B, (3-

or D including a source of power and a signal stand, which, in the arrangement .shown, in-

provided other circuits for the train control s stem which are indicated by heavier lines. hese two groups of circuits cooperate in the signalling and the train control systems, but

are shown in this manner to indicate the facility with which the train control system of this invention-may be incorporated in existing block s'ignalling systems. i

In accordance withthe existing practice, the tracks of each.block section are normally connected to a track battery 5 located at a wayside block signal station, which battery is electrically-connected to the rails at the exit end of its block section through suitable reversing switches, such as 6, tq'close a circuit for a .polar neutral relay bridged across tracks 1 and 2 at the entrance of the block controlled by the operation of the signalling arm 4, as follows from one pole of the battery 5, through conductor 7 to rail 1 and from the other pole of the battery, through the conductor 8, series relay 9 and conductor 10 to track rail 2. The normal flow of current through the circuit just traced when the track rails of the block are unoccupied is limited by the comparatively high resistance of the relay 11 to a value which is insufiicient to operate the relay 9, this relay 9 having windings of comparatively low resistance. When, however, the track rails 1 and 2 are connected by the wheels and axles of a train or vehicle in the block, the high resistance winding of the relay 11 is shunted by the low resistance path comprising these wheels and axles, and

the current flowingthrough the relay 9 is thereby increased to an amount suflicient to cause the operation of this relay, for a purpose to' be hereinafter described.

At the entrance of each block section, there, is provided a polar neutral relay 11, the structure of which is well known, and which is normallyenergized b the flow of current from the track battery ust referred to flowing through the track rails 1 and 2 to which it is electrically connected by wires 12 and 13. At the wayside station, there is also provided a local battery 14, which is connected to the I operating mechanism of the signal arm 4 through the armatures of the associated polar neutral relay 111 in such manner that whena train occupies a block section the signal 4 at the entrance of such occupied blocksection drops to ,danger position. When, however, a train occupies the block one section in advance, the signal 4 is placed in its 45 positron, indicating caution, and when neither of these blocks is occupied, the signal 4 is raised to its 90 position indicating clear.

The electrical circuits and mechanism for controlling these movements are diagramgear 19, are mounted. This gear, which rotates the shaft 15 is driven by an electric motor, such as 20 and the cam 18 is arranged to operate levers 21 and 22 so that when the arm 4 is raised to the 45 or 90 positions, respectively, the lever 21, connected to the arm 23 actuates the reversing switches 6 and 24 whereby these switches are moved clockwise to one position when the arm 4 is raised to the'45 position. The lever 22, which is also actuated by the cam .18, is connected by a rod 25to the switch 26 so that this switch is moved in a clock-wise direction when the signal arm 4 is raised to its 90 position. Suitable magnets 27 and 28 provided with pawls 29 and 30 on their respective armatures are adapted to engage suitable latches and support the arm 4 in its various positions, the latch 16 serving to hold the signal arm 4 at the 45 position .and the latch 17 functioning to support the signal arm-4 at the 90 position.

When a block section such as C is in a clear condition, a circuit is closed from one side of the battery 14 at B, conductor 31, winding of magnet 28, conductor 36, armature 11 conductor 35, armature 11-, conductor 34, armature 33 of magnet 33, energized as hereinafter described to the other side of battery 14. With the magnet 28 thus energized, its pawl 30 engages the latch 17 to hold the semaphore arm 4 in the 90 or clear indicating position. As soon as a train occupies the block section C, the wheels and axle of the locomotive shunt the current to the relay 11 at B,causing it to. open the circuit last described at its armature 11", which effects the de-energization of the magnet 28, resulting in the withdrawal of its pawl 30 which permits the semaphore arm 4 to drop under the action of gravity to its horizontal or danger indicating position. At the same time, the cam 18, previously referred to,

operates the levers 21 and 22 to move the switches 6,.24 and 26 in a counter-clockwise {lirection to the positions indicated in dotted mes.

After the train has passed to block section D, the relay 11 at B again becomes energized, in this instanceby reversed battery current, since the switch 6, at the preceding wayside station C is in its counter-clockwise position since the signal arm 4 thereat is in its danger position. This operation of the relay 11.

at B by reversed current causes its armature 11 to close the circuit from one side of battery 14 through the armature 33?) (now closed,

' since the relay 33 is energized at this time, as

is held by magnet 27 and itspawl 29. At this time, the cam 18 operates through the lever 21 to move the switches 6 and 24 clockwise, to their alternative positions thereby opening at the switch 24 the motor circuit just described.

When the train has entered the block section beyond station D, since the signal 4 at station D has moved to its danger position, the signal 4 at the station 0 is raised to its 45 position and when its switches 6 and 24 are in their clear-caution (clockwise) position,

current flows to the relay 11 at station 18 to position its armature 11 in engagement with its contact, thereby closing a circuit to the magnet 28 and to the motor 20. This circuit is traceable from one side of the battery 14, conductor 31, winding of magnet 28, conductor 36, armature 11 and its contact, armature 11, conductor 34, armature 33?) to the other pole of the battery. The motor is actuated in multiple with the circuit just described, its circuit extending from conductor 31, motor 20, conductor 37, switch 24, conductor 38 and switch 26 to conductor Under the control of this circuit the motor 20 rotates the shaft 15 and the semaphore arm 4 at wayside station T3 to the 90 position to indicate a clear condition, at which time cam 18 through the action of lever 22 moves switch. 26 clockwise to its alternative position, thus opening the motor circuit at this point.

Signal controlling transmitter.

Tn addition to the equipment previously referred to at each wayside station, there is provided an electron discharge oscillator and controlling circuits for impressing high frequency currents of two different wavelengths upon the tracks 1 and 2 of the block section to be controlled. The oscillator consists of a three-element vacuum. tube herein referred to as an electron discharge device which is provided with a filament 42, a grid 47 and a plate 53 included in an evacuated envelope. The filament 42 is heated in a circuit completed from one pole of battery 14, rheostat 40, filament 42, conductor 56, contactand armature a of relay 9 which is energized as previously described on the approach of a train, thence from armature a to the other pole of the battery. The plate circuit of this oscillator extends from the plate 53 through the coil 54 to the positive pole of plate bat tery 39. The grid circuit extends from the grid 47, conductor 46, coil 45 to one side of the filament. The coils 45 and 54 are coupled so that the grid and plate circuits react on each other in a well known manner to produce high frequency oscillations. The variable condenser 48 is adjustable to tune the circuits of the oscillator to transmit high frequency currents of one wave length corresponding to danger, whereas the variable. condenser 49 tunes the oscillator to generate and apply hi glr frequency current of a difien ent wave length corresponding to clear to the track section whenever the polar neutral relay 11 has closed its armature 1. An additional coil 57 coupled to the coil 54 in the plate circuit of the oscillator applies the mentioned high frequency currents to the tracks 1 and 2 of the block section to the rear. The circuit through which these currents are thus applied is traceable from track 1, conductors 7 and 62, coil 61, coupling coil 57, condenser 58 and thence through conductor 10 to the track 2. llt will be noted that the condenser 63 connected between the rails l and 2 forms a by-pass for the high frequency currents connected to the tracks 1 and 2 thereby lin r iting the circuit for the high frequency currents to that portion of the track circuit between the condenser 63 and the exit end of the block section. The coil 61 in the high frequency circuit just described has two tuned circuits closely coupled to it. The first one includes a coil 65, variable condenser 69 and a hot-wire relay 67; while the second circuit includes the coil 64, variable condenser and a hot-wire relay 66. The condensers 68 and 69 are provided to tune these circuits to resonance with the clear and danger high frequency currents transmitted over the conductors 59 and 62. The relays 66 and 67 are so constructed that they are energized by the high frequency currents in resonance with the circuits in which they are included. The normal cnergizing circuit for the relay 33 may be traced as follows :-from the battery 14, conductors 31 and 71, relay 33, its contact and armature 33a, contact 72 and armature 9a, of relay 9, and conductor 32, tothe battery 14. With either relay 66 or 67 energized, the relay 33 is retained energized during the interval that its normal operating circuit traced above is interrupted at the back contact and armature a of the relay 9 when this relay is energized on the approach of a train. This holding circuit of {the relay 33 extends from one pole of the battery 14 through conductors 31 and 71, winding of relay 33 and thence through the armature and contact of either relay 66 or 67 and conductor 32 to the other pole of the battery. The last described circuit provides a safeguard in the event the oscillator fails to transmit high frequency currents through the coil 61 to properly control the appi'oachin train. In the event of such failure, both relays 66 and 67 at, for example, the signal station B, becomeinert with the result that the hold ing circuit of relay 33 traced above is opened causing this relay to become de-energized and its armature 33b opens the circuit which has been maintaining the latch magnet 27 or 28*operated so that the arm 4 drops to its danger position. With the movement of the arm 4 to the danger position, the switch 6 is reversed, thus opening the polar contacts 110 and 11d of the relay 11 at the entrance end of the block B to the rear. The opening of the contact 110 disconnects the variable condenser 49 from the grid-filament circuit of thevacuum tube 43 and thus causes the transmission of oscillations of danger frequency to the track rails 1 and 2 of the block section A through a circuit including the coupling coil 57, coil 61, conductors 62' and 7, the track rails, conductors and 59'and condenser 58. Thus the system is protected against the failure of the train control current transmitter, as the failureof a transmitter to energize the track rails of a given block section results in the transmission of a danger impulse to the track rails of thenext F section to the rear.

The relays 33 are preferably'made slow acting, as represented in the drawings, by any suitable means, so that the armatures there of do not disengage the stationary front contacts for a predetermined time interval after the de-energization of the relay windings. The purpose of this slow acting feature is to insure that the contacts of the relay 33- remain closed as a train enters the block sectionwith which this relay is associated. As a train enters a given block section, say, the sectionB, the relay 9 is energized, raising its armature 9a. As the armature 9a disengages its back contact 72, the normal energizing circuit for the relayv33 is broken, and the holding circuit through the contacts of relays 66 .or 67 is not completed until the filament 42 of the vacuum tube 43 is energized by the engagement of the armature 9a with its from contact. During this period of movement of the armature 9a from its back to its front contact, the contacts of the relay 33 are maintained closed by the slow acting feature referred to above.

In-the alternative arrangement illustrated in Fig. 2, a different source of plate current is provided. In this modification a dynamo,- tor 239 is connected by wires 231 and 256 to wires 31 and 56 respectively to function whenever the vacuum tube is energized. The high voltage output of this dynamotor is connected by conductors 241 and 255 to the common conductor 41 of the plate and coil 54 respectively. In the modification shown in Fig. 3 there is indicated a wayside power line, the con- I ductors of which are designated 301 and 304.

Such an arrangement may be used where there s a cheap source of current, such as is available in hydro-electric power territory. In this arrangement, upon the ap- Sz'gnal'rcccieer.

Thehigh frequency currents, which have been impressed upon the rails 1 and 2 of a track section by the operation of the osciL later. result in the presence of a magnetic field about each of the rails as indicated in Figs. 6 and 7. The presence of this magnetic field is used to control receiving equipment on the locomotive which in turn variably controls various signals in the locomotive cab and also an elcctro-pneumatic valve to operate the air brake system of the train. In order to apply signals to a receiver, there is mounted a signal interceptor 100G attached to the locomotive bufi'er beam just ahead of the front axle but back of the pilot in the magnetic field surrounding the rail 1, while a similar signal interceptor 100R is similarly supported on the other side of the locomotive within the magnetic field surrounding the rail 2.

In the present arrangement the signal interceptors 100G and 100R are shown in the form of loops or coils, but it is to be understood that the invention is not limited to this arrangement. The signals intercepted by the coils 100G and 100R are translated by electron discharge devices 101R and 101G which actuate relays to light various signals in the' cab .and to effect train control valves by means ofcertain circuits which are illustrated in Figs. 1 and 1. It will be noted that the collector loop 100R is included in the input circuit terminating in the grid and filament of the electron discharge tube 101R, while the loop collector 100Gis included in the input circuit terminatine inthe grid and filament of the electron discharge tube 101G. The loop collector 100G is shunted'by the variable condenser 102G which serves to tune the input circuit of its electron discharge device into resonance with the high frequency waves transmitted by the oscillator, indicating a clear condition. Similarly the loop collector 100R is shunted by a variable condenser 102R which likewise serves to tune the input-circuit of its electron discharge device to resonance with the high frequency currents indicating a danger condition.

The filaments of electron discharge devices 101R and 101G are heated in series by current from a double voltage head light generator 109 which applies this heating current over conductor 112, rheostat .131, and thence through the filaments in series, conductor 122, resistance 123, to the other terminal of the generator.

The grid condenser 103R in series with the mentioned input circuit applies potential corresponding to the high frequency signalling Waves on the grid of the electron discharge, tube 101R, during the period that the loop collector coil 100R on the locomotive is in the magnetic field' of the energizedzone of the track rail circuit. The grid leak 104R in the form of a high resistance connected between the grid and filament allows the negative charge to leak from the grid when the collector coil 100R.has passed out of themagnetic field. A similar grid condenser 103G and a grid leak 104G function in a similar manner in connection with the electron discharge device 101G.

Normally a plate current is flowing in the plate circuit extending from the plate of the electron discharge device 101G, over conductor 106, winding of relay 107G, conductors 151 and 108, high ..,voltage positive terminal of the headlight generator l09and thence over conductor 122, through the filament of device 101R to the filament of the electron discharge device 101G. Similarly, plate ourrent flows in a circuit extending from the plate of the electron discharge device 101R, through the winding of relay 107R, conductor 110, armature 107 RZ), conductor 108- to the high voltage side of the generator 109 and thence over conductor 122 to the filament just mentioned. It should, be pointed out at this time that the relay 107 R of this plate circuit is initially energized through the. contact c of'the lock switch 136, which is closed manually by a key while the locomotive is in nonsignalling I territory, this circuit being traceable as follows: from the generator 109 to contact 0 of the switch 136, conductor 110, relay 107 R, to the plate of' the vacuum tube 101R, and thence from the filament of this,

the plate circuit including the relay 107R.

During the interval that the relay 107R is deenergized, its armature a closes a circuit from the generator 109, conductor 192, normal contacts of the key 111, conductor 113, armature a and back contact of relay 107R,

conductor 120, relay 121, and conductor 122,

to the generator 109. The momentary ener gization of this relay 121 closes a locking circuit for itself from conductor-120 through armature 121a, conductor 124, armature 107Ga to conductor 112, thereby retaining itself locked energized until this last described circuit is opened by the reception of a clear signal which effects the de-energization of the relay 107G. When the relay'107Gr retracts its armature a, the holding circuit for the relay 121 is opened, eflecting the deenergization of this relay.

, The relay 121 when energized closes a circuit from conductor 112, armature 121B, conductor 125, and the red cab light 126R, thence through conductor 127, resistance 128 to generator 109. The lighting of this cab light is a danger signal operated by the receipt of high frequency current which is effective to indicate the danger condition. When,however, the clear condition exists, the high frequency current to which the electron -discharge device 101G is responsive, effects the operation of this device which momentarily de-energizes relay 107G to close a circuit from generator 109 over conductor 112 through armature 107 Ga, conductor 129 to the green cab light 126G and thence to conductor 127, to the other terminal of the generator. From this it will be seen that the green cab light is a brief indication existing only during the interval that the coil 100G is in the field of a clear signal and during this interval the circuit of relay 121 is opened at the armature of relay 107G.. At this time choke 'coil 130 is shunted across the conductors'112 and 124 to protect the contact points of armature 107G-a.

The filament circuit of electron discharge devices 101R and 101G includes the resistance 131 connecting conductor 112 to conductor 122, including both of the filaments in series. It will thus be seen that the failure of either filament opens the plate circuit of both'electron discharge devices, resulting in de-energizing relays 107R and 107G. The-vehicle brakes are controlled by an electro-pneumatic valve, which is opened to effect a brake application as hereinafter described, by the de-energization of the valve magnet 118. The magnet 118 is normally energized through the following circuit from the generator 109, conductor 119, winding of the magnet 118, air switch 117, conductor 116, the normal contacts of the reset key 115,.conductor 114, armature 107R"a, conductor 113, normal contacts of forestalling key 111, and conductor 192, to the generator 109. Thus the de-energization of the relay 107R breaks the energized circuit to the magnet 118, and causes a brake application acting to stop the train, unless the engine man forestalls this action by depressing the key 111 as hereinafter described.

The mentioned forestalling key nor- 'valve is inoperative to apply the air brakes.

1 signal arm 4 at section, B to 45 mally closes a circuit from the low voltage terminals of the generator 109 through conductors 112 and 113, armature 107Ra, conductor 114, normal contacts of the reset key 115, thence througlr conductor 116 and air operated switch 117 (shown in\ detail in Fig. 12) through the magnet 118 of the electro-pneumatio valve mechanism and conductor 119, to the generator. In this way the mechanism 118 is held actuated and its The circuit for the magnet of the valve mechanism 118 is thus controlled at the armature of relay 107R so that if'a danger signal is received, this relay opens the holding circuit of'the valve mechanism 118 and if the forestalling key is not promptly depressed, the magnet of the mechanism becomes de-energized to set into operation the air brake mechanism (shown in detail in Fig. 11).

As soon as the danger signal 126R is lighted, the engineman must depress forestalling key 111 promptly in order to forestall application of the air brakes. .The airoperated switch 117 is adapted, as will be described, to open the circuit including conductor 116 and the electro-pneumatic valve 118, after a predetermined interval, during which interval the forestalling key must be depressed since after the circuit is opened at switch 117 it cannot be closed agaln by depressing the forestalling key 111, but may be closed by using the reset key 115. This last key, when depressed, momentarily connects conductor 114 to conductor 134, and

thence through armature 121-0 and conductor.

135, which connection just traced serves as a shunt around the switch 117 and thereby prevents. de en'ergization of the valve mechanism'118. This reset key115 may be sealed to prevent common use as the forestalling key is sufiici'ent if the engineman is alert.

In the system as shown in Figs. 1 to 1 inelusive, the signal at station D indicates a clear condition ahead and the train 155 adjacent that block station .is intercepting on itsloop collector 100G, the high frequency Wave indicating a clear condition through the thermionic device 101G and. the relay 107G which eflects the lighting of the green cab signal 126G to show the clear condition. The axle of the train 155 short-circuits the battery 50f block stationD to de-ener'gize the lar neutral relay 11 at the block signal 1 statlon C which drops its semaphore signal 4 to the danger position. Since no train occupies the block section C, the battery 5 connected through the track circuit by the reversing switch 6 in block section 0 energizes the rela 11 at station B; to move its armatures c and Jcounter-clockwise, which raises the indicating a caution condition. This operation -of the last mentioned semaphore arm moves switch 6 at station Bcto its normal position, which normally would position the signal arm 4; at block station A to indicate a clear condition. At this time, however, there is a train 156 passing the signal station at block A and its axles are also across the rails 1 and 2 in block section B thereby short-circuiting them and effecting the de-ener'gization of the polai neutral relay 11 at station A. This relay 11 on de-energization causes the semaphore arm 4 at station A to pass to the danger position and the oscillator at that wayside station transmits high frequency current corresponding to the danger condition from the time the loop collector coils 100 have passed the insulating joints 3-3 until all the axles of the train have passed these joints.

As an additional safety precaution against failure of the locomotive equipment, the circuits through the forestalling key and reset key when in normal position are arranged to prevent improper use, such as plugging or tying down to avoid the necessity of acknowledging the danger signal. If the forestalling key 111 is tied down, the circuit to'the electropneumatic valve 118 is opened between conductors 113 and 116 thereby deenergizing the electropneumatic valve. If the reset key 115 is tied down while the relay 121 is energized, the first clear signal which de-energizes said relay opens the circuit between conductors 134 and 135 at the armature 1210, to eflect the de-energization of the electropneumatic valve 118. It will be understood that the de-energization of this valve by either of the above methods results in the automatic application of the brakes.

The locomotive equipment as shown in Fig. 2 is the same as that of Fig. 1 except that two batteries 209 and 309 are used to supply current to the filaments and plate voltage for the electron discharge devices instead of the double voltage generator shown in Fig. 1.

The locomotive equipment shown in Fig. 3 is slightly different from that shown in the other figures and illustrates a safety feature which may be incorporated in the circuit of the loop collector coil such as 100R. If the danger loop collector coil 100R should become displaced, it might be impossible for this coil to receive a danger impulse from the track, and in order to insure that the mechanical displacement of this collector coil, as well as a break in its electrical circuit, will produce a stopping effect on the vehicle, the energizing'circuit for the filaments of the electron, discharge devices is connected in series with-the coil 100R, and a switch 300 is included in this circuit. Thisswitch 300 is suitably arranged to be opened bya mechanical displacement of the loop collector coil, and it will be apparent that with this arrange- 'ment, a displacement of the coil 100R, or a 

